1. What is stacking factor?
a) the allowance made for the power loss
b) the allowance made for the space loss between laminations
c) the allowance made for the heat loss between laminations
d) the allowance made for the power loss between laminations
Explanation: The net cross sectional area is obtained from the dimensions of various packets and an allowance is made for the space lost between laminations. This allowance is called stacking factor.
2. What is utilization factor?
a) utilization factor= cross sectional area + gross area of the core
b) utilization factor= cross sectional area – gross area of the core
c) utilization factor= cross sectional area * gross area of the core
d) utilization factor= cross sectional area / gross area of the core
Explanation: The utilization factor is equal to the ratio of the cross sectional area to the gross area of the core. The cross sectional area and the gross area of the core are first found out, and the ratio gives utilization factor.
3. What is the relationship between utilization factor and the number of core steps?
a) utilization factor is directly proportional to the number of core steps
b) utilization factor is indirectly proportional to the number of core steps
c) utilization factor is indirectly proportional to the square of number of core steps
d) utilization factor is directly proportional to the square of number of core steps
Explanation: The utilization factor increases with the increase in the number of core steps used. This eventually increases the manufacturing cost.
4. What is the optimum number of steps for small and large transformers?
a) 5, 10
b) 10, 15
c) 6, 15
d) 1, 10
Explanation: The optimum number of steps used for the large transformers is maximum of 15. The optimum number of steps for the small transformers is maximum of 6.
5. What happens if the utilization factor gets improved?
a) core area increases and the volt/turns decreases
b) core area increases and the volt/turns increases
c) core area decreases and the volt/turn decreases
d) core area decreases and the volt/turn increases
Explanation: When the utilization factor increases the core area gets increased. This leads to the increase in the volt/turn for any particular core diameter and specified flux density.
6. How many types of cores are available for core type of transformer?
a) 2
b) 3
c) 4
d) 5
Explanation: There are basically 3 types of core section available for core type of transformer. They are rectangular, square or stepped type of core sections
7. What type of core section is used for shell type transformer?
a) rectangular
b) square
c) stepped
d) cruciform
Explanation: Shell type transformers prefer only rectangular core section. Shell type transformer are moderate and low voltage transformer which use only rectangular core section.
8. What is the range of the ratio of depth to width of core in rectangular core?
a) 1-2
b) 1.5-2.5
c) 1.4-2
d) 1.5-2
Explanation: In rectangular core, the ratio of the depth to core should be minimum 1.4. The maximum value of ratio of depth to core is 2.
9. When is square and stepped cores used?
a) when circular coils are required for low voltage distribution
b) when rectangular coils are required for low voltage distribution
c) when circular coils are required for high voltage distribution
d) when rectangular coils are required for high voltage distribution
Explanation: Circular coils are required for high voltage distribution and power transformer. When circular coils are required square and stepped cores are used.
10. Circular coils are preferred because of their electrical characteristics.
a) true
b) false
Explanation: Circular coils are preferred because of their high mechanical strength. Their high mechanical strength allows them to be used in high voltage distribution and power transformer.